Among the various video display systems available in the art, an optical projection system is known to be capable of providing high quality displays in a large scale. In such an optical projection system, light from a lamp is uniformly illuminated onto an array of, e.g., M.times.N, actuated mirrors, wherein each of the mirrors is coupled with each of the actuators. The actuators may be made of an electrodisplacive material such as a piezoelectric or an electrostrictive material which deforms in response to an electric field applied thereto.
The reflected light beam from each of the mirrors is incident upon an aperture of, e.g., an optical baffle. By applying an electrical signal to each of the actuators, the relative position of each of the mirrors to the incident light beam is altered, thereby causing a deviation in the optical path of the reflected beam from each of the mirrors. As the optical path of each of the reflected beams is varied, the amount of light reflected from each of the mirrors which passes through the aperture is changed, thereby modulating the intensity of the beam. The modulated beams through the aperture are transmitted onto a projection screen via an appropriate optical device such as a projection lens, to thereby display an image thereon.
In FIGS. 1A to 1J, there are illustrated the manufacturing steps involved in manufacturing an array 100 of M.times.N thin film actuated mirrors 101, wherein M and N are integers, disclosed in a copending commonly owned application, U.S. Ser. No. 08/430,628, entitled "THIN FILM ACTUATED MIRROR ARRAY".
The process for manufacturing the array 100 begins with the preparation of the active matrix 102 having a top surface 120, comprising a substrate 108, an array of M.times.N transistors(not shown) and an array 109 of M.times.N connecting terminals 110, as shown in FIG. 1A.
In the subsequent step, there is formed on the top surface 120 of the active matrix 102 a thin film sacrificial layer 121 by using a sputtering or an evaporation method if the thin film sacrificial layer 121 is made of a metal, a chemical vapor deposition(CVD) or a spin coating method if the thin film sacrificial layer 121 is made of a phosphor-silicate glass(PSG), and a CVD method if the thin film sacrificial layer 121 is made of a poly-Si, as illustrated in FIG. 1B.
Subsequently, there is formed a first supporting layer 122 including the array 103 of M.times.N supporting members 104 and the thin film sacrificial layer 121, wherein the first supporting layer 122 is formed by: creating an array of M.times.N empty slots(not shown) by using a photolithography method, each of the empty slots being located around each of the connecting terminals 110; and forming a supporting member 104 in each of the empty slots located around each of the connecting terminals 110, by using a sputtering or a CVD method, as shown in FIG. 1C.
In the following step, an elastic layer 55 made of an insulating material is formed on top of the thin film sacrificial layer 121 including the supporting members 104.
Thereafter, a conduit 54 made of a metal is formed in each of the supporting members 104 by: first creating a hole(not shown), the hole extending from top of the elastic layer 55 to top of the connecting terminal 110, by using an etching method; and filling therein with the metal, as depicted in FIG. 1D.
Subsequently, as shown in FIG. 1E, a second thin film layer 123 made of an electrically conducting material is formed on top of the elastic layer 55 including the M.times.N conduits 54 by using a sputtering method. The second thin film layer 123 is electrically connected to the M.times.N transistors through the conduit 54 formed in each of the supporting members 104.
Thereafter, as shown in FIG. 1F, a thin film electrodisplacive layer 125 made of a piezoelectric material or an electrostrictive material is formed on top of the second thin film layer 123 by using a Sol-Gel, a sputtering or a CVD method to thereby form a semifinished actuating structure 150.
In the ensuing step, as depicted in FIG. 1G, the elastic layer 55, the second thin film layer 123 and the thin film electrodisplacive layer 125 of the semifinished actuating structure 150 are patterned by using a photolithography or a laser trimming method until the first supporting layer 122, including the array 103 of M.times.N supporting members 104 and the thin film sacrificial layer 121, is exposed to thereby form an array 151 of M.times.N semifinished actuated mirror structures 152, wherein each of the semifinished actuated mirror structures 152 includes an electrodisplacive layer 154, a second electrode layer 153 and an elastic member 155.
Thereafter, the electrodisplacive layer 154 in each of the semifinished actuated mirror structures 152 is heat treated to allow a phase transition to take place.
In the subsequent step, as depicted in FIG. 1H, a first electrode layer 126 made of an electrically conducting and light reflecting material is formed on top of the electrodisplacive layer 154 in each of the semifinished actuated mirror structures 152 by using a sputtering method, resulting in an array 164 of M.times.N actuated mirror structures 166, wherein each of the actuated mirror structures 166 includes a top and four side surfaces.
In the following step, the top and the four side surfaces in each of the actuated mirror structures 166 are completely covered with a thin film protection layer 160 made of a photoresist, SiO.sub.2 or silicon nitride to thereby form an array 167 of M.times.N protected actuated mirror structures 168, as shown in FIG. 1I.
The thin film sacrificial layer 121 of the first supporting layer 122 is then removed by using an etching method. The removal of the thin film sacrificial layer 121 in each of the protected actuated mirror structures 168 is followed by the removal of the thin film protected layer 160 therein, to thereby form the array 100 of M.times.N thin film actuated mirrors 101, as shown in FIG. 1J.
There are a number of problems associated with the above described method for manufacturing the array 100 of M.times.N thin film actuated mirrors 101. The first and foremost to be mentioned is the formation of the thin film protection layer 160 which may further compound the already complicated overall manufacturing process.
Furthermore, the etchant or the chemical used in the removal of the thin film sacrificial layer 121 of the first supporting layer 122 might chemically attack the thin film layers constituting the thin film actuated mirrors 101, degrading the structural integrity and the performance thereof which will, in turn, degrade the overall performance of the array 100.